Cline/Kline is much better than Klein. Klein does mean small in German -> and I mean every day German not old German that nobody uses anymore. Imagine if someone named you Small. "Hey Small how you doing?" "Hi, my name is Small", "Small is 6 foot 3. How ironic?" For that reason I also prefer Cline to Kline but I agree with pp'ers. There are so many great names that have a similar feel to Cline that don't feel so surnamey that are under used and have the added bonus of being gender defining.
I love the idea of Clive, Clyde or Colin for a boy or Clia/Clio, or Colleen/Coline for a girl.

for a girl CaroLINE/KaroLINE could work as well. Then Cline/Kline could be a nn if you really loved it.

Klein

My husband and I like the name Klein for a boy , but it has made me question the name after reading some of the comments. For instance it meaning small in German. We also like the names Nixon - I like Rowan, but the only name we agreed on before I researched was Klein

One of my favorite high school teachers was Miss Klein. She is like 6 feet tall and a German immigrant. She laughed at the irony of her own name, but it was her last name. As a first name, it definitely feels male. I would use it if you love it. It's not a "bad" name, a little awkward if you move to Germany... but not BAD. Also, my teacher was really young and cool, so we students often dropped the "Miss" and just referred to her as Klein, so it's totally functional.

Also, I think Klein is WAY better than Nixon. Most people do not know that Klein means small. Almost everyone thinks of the watergate scandal and unattractive RichardNixon when they hear Nixon, sorry. Plus "nix" is an ENGLISH word that means to cancel, get rid of, or nothing. Maybe Nick or even Nickson instead?